1. Field of the Invention
The present invention relates to a power storage device and an electrode thereof.
Note that, in this specification, the power storage device refers to every element and every device which have a function of storing power.
2. Description of the Related Art
In recent years, power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air cells have been actively developed. Further, it has been proposed that such power storage devices be used in a variety of electric appliances such as a refrigerator (see Patent Document 1), an air conditioner (see Patent Document 2), an indoor lighting device (see Patent Document 3), and a microwave oven (see Patent Document 4).
An electrode for the power storage device is manufactured by forming an active material over a surface of a current collector, for example. As an active material which occludes lithium, a material which can occlude and release ions serving as carriers, such as carbon or silicon, is used. In particular, silicon has attracted attention because it has a higher theoretical capacity than carbon and is advantageous in increasing the capacities of power storage devices.
For example, Non-Patent Document 1 discloses a lithium-ion secondary battery whose positive electrode is formed using whisker-like single crystal silicon. Non-Patent Document 1 suggests that when whisker-like single crystal silicon is used, the structure of the electrode is not easily damaged even when the volume of silicon is changed due to occlusion and release of lithium ions, resulting in increases in charge/discharge characteristics.